1. Field of the Invention
The present invention relates to an optical system and, more particularly, to an optical system for use in a projection display.
2. Description of the Prior Art
The development of electro-optical technology is tending to visualize information, and the key factor of determining projection-type imaging quality usually depends on the quality of an optical system of a projection display. Considering the production cost, how to produce a portable projection display with high clarity for promoting the market competition is always the focus of research and development in the electro-optical industry.
Referring to FIG. 1, an optical system 10 of a conventional projection display includes a light source 11 for producing a white light beam. The light beam is reflected by a reflector 12 and converges onto a color-generating device 13, such as a color wheel. The color-generating device 13 comprising a series of red, green, and blue filters sequentially converts the color of the light beam into red, green, and blue primaries when the light beam passes through it. A first condenser lens 141 and a second condenser lens 142 after the color-generating device 13 are used for converging and transmitting the light beam. The light beam is reflected upward by a first mirror 151 for passing through a third condenser lens 143, and then reflected by a second mirror 152 for passing through a fourth condenser lens 144 to impinge onto a digital micro-mirror device (DMD) 16. The DMD 16 has a two-dimensional array of micro-mirrors. Each micro-mirror with the tilt angles about xc2x112 degree varies the angle of reflection of the light beam reflected therefrom and thereby causes on/off state. When the micro-minor switches to on-state, the light beam is reflected to enter a projection lens 17 for projecting on a screen (not shown). When the micro-mirror switches to off-state, the light beam is reflected away from the projection lens 17 to avoid projecting on the screen. Therefore, the necessary light beam can be properly selected to be projected on the screen.
As shown in FIG. 2, the third condenser lens 143 of the conventional optical system 10 is generally as close as possible to the optical axis between the DMD 16 and the projection lens 17, so as to form a more compact optical system 10. However, parts of the light beam from the third condenser lens 143 to the second mirror 152 will very possibly be obstructed by the projection lens 17 relatively. Thus, this obstruction causes a mechanical and optical interference such that the illumination efficiency of the projection display is degraded. To avoid the obstruction in the conventional projection display, the projection lens 17 moves toward the screen 18 to a position 17xe2x80x2, or the third condenser lens 143 moves outward to a position 143 Therefore, all above-mentioned adjustments elongate the light path of the optical system 10 and result in a bulky projection display.
In addition, the light beam in the conventional optical system 10 passes through three condenser lens 141, 142, and 143 as well as two mirrors 151 and 152 to impinge onto the DMD 16. The conventional optical system 10 needs excessive components and results in not only a complex optical structure but increasing the production cost, elongating the light path, and enlarging the bulk of the optical system 10. Therefore, there are many defects in the conventional projection display needed to be improved.
An objective of the present invention is to provide an optical system that has a total reflection lens for avoiding the interference to raise the projection efficiency and image quality.
Another objective of the present invention is to provide an optical system that reduces some optical components to simplify and compact the whole projection display.
To achieve the above objectives, the optical system of the present invention disposes a total reflection lens between a light valve and a projection lens. When a white light beam from a light source passes through a color wheel, the color of the light beam is sequentially converted into red, green, and blue primaries, and uniformed by an integrator. Then, the light beam impinges into the total reflection lens and is reflected to the light valve therefrom. The light valve reflects the light beam into a projection lens to be projected on a screen. Therefore, this invention increases the projection efficiency and reduces the volume and components of the optical system.